The present invention relates to voltage-to-current signal converters, and more particularly, converters having differential inputs to receive voltage signals for conversion to current flows at the output in a direction depending on input differential signal polarity.
A number of uses have been found for circuits which can convert a voltage signal supplied at the circuit input to a corresponding current at the circuit output. Such uses include, for instance, the testing of other electronic circuits or components at various current levels, and for providing controllable currents to certain kinds of circuits which are to be supplied such currents during operation of the system in which they are included.
A number of different circuit configurations are known for these purposes. In many instances, the use of a differential voltage input is quite desirable because precise conversions can be made based on the voltage difference at the inputs while the voltage portions common to the signal of each input are ignored. In many instances, the differential voltage between two voltage signals may be much less than the full value of either of the signals. In these circumstances, extremely high common mode rejection ratios and power supply variation rejection ratios are necessary. Further, a high input impedance is required to avoid placing any kind of loading on such signal sources.
Many of the known circuits for this kind of conversion are based primarily on operational amplifiers and either cannot, or cannot without great difficulty and expense, satisfy such stringent performance characteristics. Furthermore, many of these circuits, to be able to meet such performance requirements, would need to rely on measures which are not easily compatible with forming the circuits as monolithic integrated circuits.